FTP server returned 500 error with ASP.NET C#

Question

I 'm developing FTP exe ASP.NET、C#2.0 .

but I FTP server returned 500 error This command execute everyday. but this error is o**ccured only twice** on the month. What's wrong?

Answer 1

Is there a firewall sitting between the source and destination?

http://support.microsoft.com/kb/281193

Answer 2

FTP 500 is an "Invalid PORT Command". As FTP uses a separate Port for data transfer, likely your FTP Client tried to pass in an invalid port.

When the error occurs, write down the port, decode it, that your client sent and verify that a) it's valid and b) that it's open.